Fan



P 28, 1954 K. F. A. MUHLBERG 93 FAN Filed Jan. 20, 1951 er wavmnrir Patented Sept. 28, 1954 FAN Kurt F. A. Muhlberg, 'Cochituate, Mass., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 20, 1951, Serial No. 206,952

4 Claims.

This invention relates to fans having axial inlets, and relates more particularly to duct connections at the axial inlets of such fans for admitting secondary air thereinto without adversely afiectin the performances of the fans.

For maximum performance, the axial inlet of a fan must be nicely streamlined with no obstructions to gas flow extending thereinto. However, for some duties, it is necessary to supply secondary air into a fan inlet through a supply duct; and, in the past, such supply ducts, when not used for supplying secondary air have extended into the fan inlets and have obstructed the flow thereinto. An example of such a duty is the supply of air through an air heater for the combustion chamber of a steam-power plant. The air supplied by a fan is drawn from the apparatus room in which the fan is located, and blown through the interiors of heat-exchange tubes, over the exteriors of which, the flue gases of the plant pass. At low plant loads, the temperature of the inlet header sheet of the air heater may fall below the dew point temperature of the corrosive vapors in the flue gases, resulting in the condensation of such vapors on the header sheet with resulting corrosion. Accordingly, it has been the practice at low plant loads to recirculate heated air from the outlet of the air heater into the inlet of the fan for maintaining a large volume of heated air through the heater. Recirculation ducts have extended into the inlets of the fans and have interfered with the flow of air thereinto when no recirculation was required.

The G-eissler et a1. Patent No. 2,476,543 discloses one efficient method of supplying secondary air into the axial inlet of a fan without afiecting the performance of the fan when the supply of secondary air is discontinued, but requires a special form of duct for accomplishing this, such a duct usually having to be fabricated and installed after installation of a fan.

This invention provides duct connections for supplyin secondary air efflciently into the axial inlet of a fan, which are built into the inlet of the fan at the time it is fabricated, requiring only the connection of an ordinary duct when the fan is installed. This invention is particularly suited for use with centrifugal fans having spin vanes such as are disclosed in the H. F. Hagen Patent No. 1,989,413.

An object of this invention is to provide in the axial inlet of a fan, a duct connection for secondary air which does not interfere with the flow of primary air thereinto.

The invention will now be described with reference to the drawing, of which:

Fig. 1 is a side elevation, in section, of a centrifugal fan embodying this invention;

Fig. 2 is a partial view, in section, illustrating a modification of the fan of Fig. l, and

Fig. 3 is a partial view looking into the inlet of the fan of Fig. 1.

The fan illustrated is a centrifugal fan having the scroll casing !0 containin the fan wheel ll mounted on the rotary shaft l2 which is supported in end bearings l3, only one of which is illustrated.

The fan has the inlet shroud l4 forming an axial inlet passage which converges towards the wheel l i. The spin vanes [5 are pivoted in this passage on pivot rods which are rotatably supported at their outer ends in the shroud l4, and at their inner ends within the housing- [6 around the shaft I2, and which contains vane rotating mechanism for rotating the vanes through the adjusting rods H, as disclosed in detail in the E. L. Richardson Patent No. 2,100,489.

The fan described so far with reference to the drawing, is conventional. This invention adds to such a fan the constructions shown by the drawing for providing a secondary air passage into the fan inlet.

Referring first to Figs. 1 and 3 of the drawing, the outer end of the sheet (9 is connected to the casing wall 22 which is the inner wall of an annular, secondary air passage 23 extendin around the inlet of the fan, and which has therearound the sheet 24 having a portion extending along horizontal lines connected to the sheet 22, and having another portion extending along vertical lines connected to the shroud 24. The passage 23 has the circular perforated sheeet 25 between same and the passage 2i for providing uniform distribution of air from the passage 23 into the passage 19, the perforations in the sheet serving as constrictions causing pressure to be built up in the passage 23.

The upper portion of the casing II! has the duct sheet 25 spaced from the wall 22 and connected to the shroud l4, and forming with the walls 22 and 31, an inlet duct 21 for secondary air, which discharges into the passage 23, the horizontally extending portion of the sheet 24 being omitted at the duct 21.

The walls 26 and 28 extend above the casing and terminate in the flange 29 which is secured to the lower flange 30 of the damper duct 3!, the upper flan e 32 of which is secured to the flange 33 of the duct 34 which is connected to a source of secondary air such as the air heater referred to and illustrated in said Geissler et a1. patent. The damper duct contains a damper 36 which may be adjusted to regulate the volume of secondary air.

The walls of the secondary air passage 2| do not protrude into the fan inlet, and do not, therefore, interfere with the flow therethrough of primary air.

Fig. 2 of the drawing illustrates another "em bodimeht of the invention in which the inlet shroud 4c in which the spin vanes l5 are pivoted,

terminates short of the inlet of the fan wheel," and the sheet H spaced therefrom extends past the inner end thereof into the inlet of the fan wheel. The space between the inner edge of the shroud and the sheet 41 per f'orms'the function of the slots it of Fig. 1 in admitting gas from the secondary air passage 2! intothe fan wheel. The inner portion of the sheet 6''] also performs the function of the inner portion of the shroud 14 of Fig. l in that it guides the primary as well as the secondary air, smoothly into the fan wheel.

It should be apparent that in both the illushated-embodiments of the invention, the sec ondary air passage, where it terminates in the fan inlet, offers no obstructions to the flow of primary air into the inlet, nor impedes in any way "the action of the spin vanes in causing the primary air to spin when they are adjusted toward closed position as described in said Hagen patent.

The secondary air passages can be built into the I fan when the latter is fabricated with but slight additional cost, and eliminates the necessity for fabricating and installing duct terminations of the type disclosed in said Geissler patent at the installation site of the fan. While the embodiments of the invention have been described for thepurpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement of a 'iparatus illustrated, since modifications thereof maybe suggested by those skilled in the art, without departure from the essence of the invention.

Whatl claim as my invention, is:

1."In a centrifugal fan havin a casing, a-fan wheel in the casing, and a shroud sheet forming a converging, axial, primary gas passage into said wheel, said shroud sheet-having an outwardly turned portion at the inlet to said passage, ex-

tending substantially perpendicular to the axis of said wheel, the combination of an inner sheet, substantially conical in section, Within said casing and extending around a portion of said shroud sheet and formin therewith a converging secondary gas passage discharging into said primary passage, said inner sheet having an outer end spaced from said outwardly turned sheet portion and forming therewith a circumferentially extending inlet into said converging secondary gas passage; means including spaced-apart sheets extending substantially perpendicular to said axis and connecting with said outer end of said inner sheet and said outwardly turned portion of said lar chamber.

3. The invention claimed in claim 1 in which the inner end of the inner sheet contacts the shroud sheet, and in which a plurality of spacedapart slots are'provided in the shroud sheet adiacent the contact therewith of said inner end of inner sheet but outwardly thereof, and through which secondary gas is discharged into said primary passage.

4. The invention claimed in claim 3 in which a circular perforated. sheet extends between said circumferentially extending inlet and said annular chamber.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,467,306 Carrier Sept. 11, 1923 1,787,655 Anderson Jan. 6, 1931 2,215,901 Cl'llistman -Sept. 24, 1940 2,287,822 Odor et a1 June 30, 1942 2,297,275 Acheson Sept. 29, 1942 

